An example of an existing multi-air-conditioning system for a building includes an air-conditioning apparatus including an outdoor unit, which is a heat source unit disposed outdoors, and an indoor unit disposed indoors. The air-conditioning apparatus performs a cooling operation or a heating operation by circulating a refrigerant between the outdoor unit and the indoor unit and conveying cooling energy or heating energy to an air-conditioned space, such as the inside of a room. In such an air-conditioning apparatus, HFC refrigerants, for example, are widely used as the refrigerant. Also, natural refrigerants, such as carbon dioxide, have been used in recent years.
A chiller system is a typical example of an existing air-conditioning apparatus having another configuration. In this air-conditioning apparatus, a cooling operation or a heating operation is performed by generating cooling energy or heating energy in a heat source unit disposed outdoors, transferring the cooling energy or heating energy to a heat medium, such as water or antifreezing fluid, in a heat exchanger arranged in the outdoor unit, and conveying the heat medium to a fan coil unit, a panel heater, or the like, which is an indoor unit arranged in an air-conditioned space, through a heat medium circuit (see, for example, Patent Literature 1).
With the air-conditioning apparatus described in Patent Literature 1, there has been a risk that a user will be adversely affected if the refrigerant leaks into the room. Therefore, as an example of an air-conditioning apparatus according to the related art in which the refrigerant is circulated through the indoor unit, an air-conditioning apparatus capable of detecting a leakage of the refrigerant into the room (from a use-side heat exchanger or a pipe disposed near the use-side heat exchanger) has been proposed. For example, an apparatus has been proposed which includes “a single heat source unit A including a compressor 1, a four-way switching valve 2 that switches a passage of a refrigerant discharged from the compressor, and a heat-source-unit-side heat exchanger 3; a plurality of indoor units B, C, and D, each of which includes an indoor-side heat exchanger 5 and a flow-rate control device 9; and a relay unit including a first branch portion 10, valve devices 20, and a second branch portion 11, the first branch portion 10 connecting the heat source unit to the indoor units with first and second connection pipes 6 and 7 and including valve devices 8a and 8b that connect one end of each indoor-side heat exchanger to one of the first and second connection pipes in a switchable manner, each valve device 20 being connected to the other end of the corresponding indoor-side heat exchanger, and the second branch portion 11 being capable of connecting the other end of each indoor-side heat exchanger to the second connection pipe through check valves 17 and 18 connected to the corresponding valve device” (see, for example, Patent Literature 2).
However, the air-conditioning apparatus described in Patent Literature 2 has a problem in that detection of a leakage of the heat medium from the heat medium circuit arranged near the room is not particularly taken into consideration because, for example, the heat medium does not have a large adverse effect on the user. Accordingly, an air-conditioning apparatus has been proposed in which, with regard to a leakage of heat medium (such as water), it is determined that air that has entered in a pipe is discharged when a pump driving current changes from a value lower than or equal to a predetermined reference current value to a value above the predetermined reference current value (see, for example, Patent Literature 3).